1. Field of the Invention
This invention relates generally to penetrant devices. It particularly relates to a penetrant apparatus and method for controlling the depth that a penetrant means penetrates a material relative to its outer surface, where the cross-sectional thickness of the material is not susceptible to caliper-type measurement because its inner surface is inaccessible except by intrusive means.
2. Background of the Invention
When a procedure requires the penetration of a material to a precise depth, resort to the use of a guarded instrument is typical. In such an instrument its depth of penetration into a material is governed by the placement of a shoulder stop, which prevents further penetration of the instrument. Certain machining procedures use shoulder-stops, namely drilling operations into material stock where partial depth holes are drilled. Material removal operations on multilayer plates utilize cutting devices in combination with depth-of-cut restriction devices. Operators or technicians may also rely on acquired skill without the aid of guarded instruments or depth-of-cut restriction devices for drilling partial depth holes or for material removal operations on multilayer plates.
These methods are usually satisfactory if penetration of the material to only an approximate desired depth is required and variation in thickness of the material is not critical. However, where penetration of a material to a precise depth is critical, or where a material removal operation or cutting procedure is microscopic in nature, inherently requiring precise depth penetration with tolerences on the order of several microns, the aforesaid techniques known to the art are crude and oftentimes of unacceptable riskiness. In general material removal operations the risk is in terms of lost material and lost time.
Cutting tools and penetrant apparatus in common use cannot be used for penetrating a material whose inner surface is inaccessible, except by intrusive means, where the unpenetrated thickness of material at any point adjacent the material's inner surface is required to be precisely controlled, or to comprise a uniform proportional thickness of the material at that point. This is especially the case when the cross section of the portion of material to be penetrated is neither a constant thickness nor uniformly varying in thickness. The known guarded instruments with shoulder stops would have to be continuously adjusted as the penetrant means or cutting tool traverses the outer surface of the material, which could only be done if the thickness of the material at the point of penetration were also known. Yet, if the inner surface is inaccessible, the necessary thickness measurements are impossible, rendering use of such instruments impractical if not prohibited.
The difficulties encountered in the use of general cutting tools and penetrant apparatus just discussed become particularly acute in surgical procedures where safety and efficacy are major concerns and where any risk can be unacceptable. Surgical procedures often utilize surgical instruments of construction identical to those known in the art for penetrating of materials generally. Guarded surgical instruments use shoulder stops when penetration of a material or tissue to a certain depth is required.
Oftentimes surgical procedures require the penetration of a material or tissue in such a manner that a portion of the cross-sectional thickness of the material or tissue is left unpenetrated adjacent its inner surface, that unpenetrated portion being of a precise thickness or a uniform proportion of the thickness of the material at the point of penetration. That is, it is not uncommon for a surgical procedure to define the depth of penetration of a penetrant means with respect to a reference inner surface.
Typically, though, the material or tissue having a defined outer surface and inner surface is not susceptible to a caliper-type measurement because the inner surface is inaccessible except by intrusive means. Also, for any given portion of material or tissue, the cross-sectional thickness is often not constant and ordinarily varies in a nonuniform manner.
Variation in the cross-sectional thickness of a material is not a critical factor when the penetration of the material or tissue involves the insertion of a needle or a probe so as to leave unpenetrated a precise thickness or a uniform proportion of the thickness of the material at the point of penetration. The insertion of a needle or probe in the situation just described, however, requires the simultaneous thickness measurement of the material or tissue and the measurement of the depth of penetration of the needle or probe at the point of penetration
Variation of the cross-sectional thickness of a material becomes a factor when the penetration effected is an incision. With an incision, not only must the thickness measurement of the material or tissue be simultaneous with the measurement of the depth of penetration of the penetrant means, but, as the cutting blade linearly incises the material or tissue while traversing the outer surface, the measurements continuously change, requiring a corresponding adjustment in depth of cut.
Another factor must be considered in the insertion of a needle or probe, as well as in a cutting blade incision. When the material or tissue is penetrated by a needle, probe or cutting blade, the material or tissue deforms at the point of penetration. Control of the penetration of the penetrant means must account for this deformation. Simultaneous measurement of the thickness of the material or tissue and measurement of the depth of penetration must also take into account this deformation of the material or tissue.
Ultrasound machines in common use can be used to measure the thickness between the outer surface of a material or tissue and a reference inner surface. Their current usefulness is limited, however, to a thickness measurement just prior to manual insertion of a needle or probe. Once the thickness between the outer surface and the reference inner surface of a material has been determined, the needle or probe is inserted at approximately the point of thickness measurement. A length of needle or probe corresponding to the desired depth of penetration is physically measured on the needle or probe using a scaled rule. Penetration beyond the measured point is usually limited by a shoulder stop. The disadvantage to this type of measurement is that the tolerances are only on the order of approximately one sixteenth of an inch; tolerances on the order of a few microns are impossible.
Skillful surgical technique is still the most efficacious procedure in the insertion of a needle or probe, or in making an incision with a cutting blade. But again, even skillful surgeons cannot consistently incise a material or tissue leaving an unpenetrated thickness of uniform or uniform proportional thickness of the material or tissue adjacent an inner surface. Indeed, when surgery is microscopic in nature, incisions to a precise depth relative to an outer surface are extremely difficult. The surgical difficulty is increased in microfine work when the unpenetrated portion of material adjacent to the inner surface must be of substantially uniform thickness or where the unpenetrated portion of material at any point adjacent to the inner surface must be a substantially uniform proportion of the material at said point.
The lack of apparatus and methods in the art affording precise and controlled placement or penetration of a penetrant means together with the combined continuous functions of thickness measurement and measurement of the depth of penetration of the penetrant means are particularly critical in surgical procedures such as radial keratotomy, amniocentesis, venous puncture, arterial puncture, aspiration of a cyst, or spinal taps.
Radial keratotomy is a new surgical procedure for correction of refractive errors in the eye of an animal, particularly humans. The procedure involves penetrating the cornea inwardly from its outer surface with a cutting blade while leaving adjacent to its inner surface an unpenetrated portion of corneal tissue. A plurality of partial thickness radial incisions of precise depth are made which traverse the cornea and which radiate from the anterior pole to the limbus. The incisions are made as deeply as possible with respect to the inner surface of the cornea (Decemet's membrane or the endothelium) without piercing it. If the knife penetrates into the anterior chamber of the eye, infection (endophthalmitis) may result. Insufficient penetration prevents surgical correction of the refractive error. Presently the depth of corneal incision is monitored by microscopic direct vision when using either guarded or unguarded cutting blades. The most successful results in the correction of refractive error occur if the thickness of cornea left uncut is a uniform number of microns from the inner surface of the cornea or a uniform proportional thickness of the original thickness.
The procedure is simple in terms of the surgical details, but is technically difficult because the average cornea is only about 500 microns thick at the anterior pole, and varies in thickness radially from the anterior pole in a nonuniform manner. In addition, the unsteadiness of even a skilled surgeon's hand at this microscopic level risks penetration into the anterior chamber of the eye and later resulting endophthalmitis.
The art does not provide a surgical instrument or method where the thickness of the cornea is continuously monitored while continuously monitoring the depth of penetration of the cutting blade in order to automatically maintain the cutting blade at the proper position from the inner surface of the cornea to within tolerances of a few microns while the traversing incisions are made.
In amniocentesis, embryonic fluid is removed from inside the womb by using a needle. Penetration of the needle to a precise depth is critical; if the needle penetrates too deeply into the womb, there is a risk of injury to the fetus.
The art does not provide a surgical instrument or method where the position of the fetus (as an reference inner surface) is discriminated and fetal position is continuously monitored while a needle is inserted into the womb to a precise distance from the fetus and while the position of the needle tip is also continuously monitored.
In venous puncture, arterial puncture, or aspiration of a cyst, a needle penetrates the near wall of a vein or artery, or the near surface of a cyst, and is further inserted so that the needle tip is fully inside the vein, artery or cyst. Further penetration is halted so that the needle does not pierce the far wall of the vein, artery or cyst. The present method of manual insertion risks the possibility of penetrating the far wall or surface. Also, if manual insertion is done too slowly the vein, artery or cyst may be displaced to one side or the walls of the vein, artery or cyst may become invaginated.
The art does not provide a surgical instrument or method for performing a venous or arterial puncture, or aspiration of a cyst, where the far wall or surface is used as the reference inner surface and the needle is inserted to a precise depth from the reference inner surface while the position of the reference inner surface and the position of the needle tip are continuously monitored.
Spinal taps require the precise placement of a needle into the spinal cord. Once penetration of the near wall of the spinal cord has been achieved, the needle is further inserted but is eventually stopped short of penetration of the far wall. The present methods of manual insertion risk the penetration of the far wall. This would require manual adjustments in the depth of needle penetration or another attempt at the spinal tap.
The art does not provide a surgical instrument or method for continuously monitoring the position of the far wall of the spinal cord in order to determine the thickness of material between the skin surface and far wall while continuously monitoring and controlling the position of the needle during insertion.
As can be appreciated by considering the aforesaid material penetration methods and the aforesaid surgical procedures, it is apparent that none of the apparatus or methods known to the art control the penetration of a material having an outer surface and a substantially inaccessible inner surface by continuously monitoring thickness and depth of penetration of the penetrant means while adjusting the depth of penetration, such that the unpenetrated portion of material adjacent to the inner surface is of substantially uniform thickness, or such that the unpenetrated portion of material at any point adjacent to the inner surface is a substantially uniform proportion of the material at said point.
As a result, there is a need in the art for a cutting tool or penetrant apparatus for penetrating a material having an outer surface and an inner surface whose inner surface is inaccessible (except by intrusive means), which apparatus adjusts the penetration of the penetrant means so that the unpenetrated portion of the material at a point adjacent to the inner surface is of substantially uniform thickness or is a substantially uniform proportion of the thickness of the material at said point. The cutting tool or penetrant apparatus would be able to cut or penetrate a material and leave a desired portion of material uncut or unpenetrated adjacent the material's inner surface both when the cross section of the portion of material to be penetrated was non-constant in thickness and when it did not vary uniformly in thickness. Furthermore, the penetrant means or cutting tool would be continuously adjusted to accommodate the varying cross-sectional thickness of the material as the cutting tool or penetrant apparatus traversed its outer surface, so that the unpenetrated portion at any point adjacent the material's inner surface would be the desired uniform thickness or the desired uniform proportional thickness of the material at that point of penetration.
Similarly, there is a need in the art for a surgical instrument for penetrating a material or tissue having an outer surface and an inner surface whose inner surface is inaccessible (except by intrusive means), which apparatus adjusts the penetration of the penetrant means so that the unpenetrated portion of the material or tissue at a point adjacent to the inner surface is of substantially uniform thickness or is a substantially uniform proportion of the thickness of the material or tissue at said point. The surgical instrument would be capable of use in microscopic surgery where penetration to a precise depth is required, as well as where the unpenetrated portion of the material or tissue at a point adjacent to the inner surface must be a substantially uniform thickness or a substantially uniform proportion of the thickness of the material or tissue at the point of penetration. Precise and controlled penetration of a penetrant means would be combined with the continuous functions of thickness measurement and measurement of the depth of penetration of the penetrant means.
More specifically, there is a need in the art for a surgical instrument for performing a radial keratotomy where the thickness of the cornea is continuously monitored and, simultaneously, the depth of penetration of the cutting blade is continuously monitored and adjusted, so that the cutting blade would be maintained at the proper position from the inner surface of the cornea to within tolerances of a few microns.
A surgical instrument for amniocentesis is also needed which would disclose and continuously monitor fetal position while controlling the insertion of a needle into the womb to a precise distance from the fetus and while continuously monitoring the position of the needle tip.
A similar demand for a surgical instrument for performing venous puncture, arterial puncture, or aspiration of a cyst which would automatically insert a needle to a precise distance from the far walls of a vein, artery or cyst (inner surfaces) also exists in the art. The insertion of the needle would be quick enough to minimize displacement of the vein, artery or cyst and to minimize the chances of invaginating the walls of the vein, artery or cyst. The position of the reference inner surface and the position of the needle tip would be continuously monitored so that adjustment of the penetration would be continuously controlled.
Finally, a requirement exists for a surgical instrument for performing spinal taps which would automatically insert a needle to a precise distance from the far wall of the spinal cord (inner surface). The position of the inner surface and the position of the needle tip would be continuously monitored so that adjustment of the penetration would be continuously controlled.